Rectifier circuits, synchronous rectifier circuits, and related electric devices

ABSTRACT

A rectifier circuit has a cathode node, an anode node, a rectifier switch, an auxiliary switch, an operating power capacitor and a rectifier controller supplied with power by the operating power capacitor. The rectifier switch is electrically connected to the auxiliary switch. When the rectifier controller turns OFF both the rectifier and auxiliary switches, the rectifier circuit supports a first loop, directing a first current to flow into the rectifier circuit from the anode node, through the operating power capacitor, and away the rectifier circuit from the cathode, so the operating power capacitor is charged. When the rectifier controller turns ON both the rectifier and auxiliary switches, the rectifier circuit supports a second loop directing a second current to flow into the rectifier circuit from the anode node, through the rectifier switch, and away the rectifier circuit from the cathode, without charging the operating power capacitor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of TaiwanApplication Series Number 109118915 filed on Jun. 5, 2020, which isincorporated by reference in its entirety.

BACKGROUND

The present disclosure relates generally to rectifier circuits, and moreparticularly to rectifier circuits that are capable of building up anoperating power voltage supplying power to a rectifier controller insidethe rectifier circuits.

Commonly known rectifier devices are diodes mostly, each having twoends: anode and cathode, for directing the current flowing a one-waypath from the anode to the cathode, but blocking the current thatotherwise flows along the opposite direction.

To make a diode conduct a current, a diode must be forward biased to acertain level. Normally speaking, a diode with a PN junction needs itsanode-to-cathode voltage more than a forward voltage, which is about 0.7volt for example, to conduct current. In view of power devices thatsupply large current to a load, a diode will constantly consumeconsiderable amount of power because the diode costs constantly 0.7Vvoltage drop to conduct that large current to the load.

A rectifier switch in company with a rectifier controller has beenintroduced to replace a diode, for the purpose of synchronousrectification. When the rectifier controller senses that two terminalsof the rectifier switch are forward biased, it turns ON the rectifierswitch to conduct a current over a channel with very little impedance.In the words, the rectifier switch is turned ON to short the twoterminals to each other. When the rectifier controller senses that thetwo terminals are reversely biased, it turns OFF the rectifier switch toDC isolate the two terminals from each other. The rectifier switch actsas an open circuit between the two terminals if it is turned OFF. Arectifier switch consumes less power during rectification in comparisonwith a diode, because the rectifier switch needs no forward voltage andthe channel of the rectifier switch has very little impedance when it isturned ON.

A rectifier controller needs however an operating power voltage thatsupplies power to the rectifier controller, so it can work as it isdesigned to. It is a common practice that a rectifier controllerutilizes an output power voltage of a power converter as its ownoperating power voltage. Nevertheless, the output power voltage of apower converter might be as low as 3.5V, especially when the powerconverter is a battery charger, and 3.5V is too low to supply power tothe rectifier controller, which normally requires its operating powervoltage with a minimum of 5V to operate properly.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 demonstrates flyback power converter 100 according to embodimentsof the invention.

FIG. 2 shows synchronous rectifier circuit 120A.

FIG. 3 demonstrates synchronous rectifier controller 102 in FIG. 2 .

FIG. 4 shows control method M01 in use of synchronous rectifier circuit120A.

FIG. 5A demonstrates loop LPA that secondary-side current I_(SEC)follows when rectifier switch NSR1 and auxiliary switch NC are turnedOFF.

FIG. 5B demonstrates loop LPB that secondary-side current I_(SEC)follows when rectifier switch NSR1 and auxiliary switch NC are turnedON.

FIG. 6A shows waveforms of signals in FIGS. 5A and 5B when operatingpower voltage VSR_(DD) is deemed over low, or operating power voltageVSR_(DD) is less than reference voltage V_(SET-L).

FIG. 6B shows waveforms of signals in FIG. 5B when operating powervoltage VSR_(DD) is good enough, or operating power voltage VSR_(DD) ishigher than reference voltage V_(SET-H).

FIG. 7 demonstrates synchronous rectifier circuit 120B, an example ofsynchronous rectifier circuit 120.

FIG. 8A demonstrates loop LPC that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.7 are turned OFF.

FIG. 8B demonstrates loop LPD that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.7 are turned ON.

FIG. 9 illustrates flyback power converter 600 according to embodimentsof the invention.

FIG. 10 shows synchronous rectifier circuit 620A, an example ofsynchronous rectifier circuit 620 in FIG. 9 .

FIG. 11A demonstrates loop LPE that secondary-side current I_(SEC)follows when rectifier switch NSR1 and auxiliary switch NC in FIG. 10are turned OFF.

FIG. 11B demonstrates loop LPF that secondary-side current I_(SEC)follows when rectifier switch NSR1 and auxiliary switch NC in FIG. 10are turned ON.

FIG. 12 shows waveforms of signals in FIGS. 11A and 11B when operatingpower voltage VSR_(DD) is deemed over low, or operating power voltageVSR_(DD) is less than reference voltage V_(SET-L).

FIG. 13 shows synchronous rectifier circuit 620B, an example ofsynchronous rectifier circuit 620 in FIG. 9 .

FIG. 14A demonstrates loop LPG that secondary-side current I_(SEC)follows when rectifier switch NSR1 and auxiliary switch NC in FIG. 13are turned OFF.

FIG. 14B demonstrates loop LPH that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.13 are turned ON.

FIG. 15 shows high-voltage electric device NSA, in which rectifierswitch NSR1 and schottky barrier diode DSK are formed and integrated ona monocrystal chip.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings. Skilled artisans willappreciate that elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale. For example,the dimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding of variousembodiments of the present invention. Also, common but well-understoodelements that are useful or necessary in a commercially feasibleembodiment are often not depicted in order to facilitate a lessobstructed view of these various embodiments of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one having ordinary skill in the art thatthe specific detail need not be employed to practice the presentinvention. In other instances, well-known materials or methods have notbeen described in detail in order to avoid obscuring the presentinvention.

Reference throughout this specification to “one embodiment”, “anembodiment”, “one example” or “an example” means that a particularfeature, structure or characteristic described in connection with theembodiment or example is included in at least one embodiment of thepresent invention. Thus, appearances of the phrases “in one embodiment”,“in an embodiment”, “one example” or “an example” in various placesthroughout this specification are not necessarily all referring to thesame embodiment or example. Furthermore, the particular features,structures or characteristics may be combined in any suitablecombinations and/or subcombinations in one or more embodiments orexamples. Particular features, structures or characteristics may beincluded in an integrated circuit, an electronic circuit, acombinational logic circuit, or other suitable components that providethe described functionality. In addition, it is appreciated that thefigures provided herewith are for explanation purposes to personsordinarily skilled in the art and that the drawings are not necessarilydrawn to scale.

According to embodiments of the invention, a rectifier circuit isdisclosed, capable of replacing a diode. The rectifier circuit has acathode node, an anode node, a rectifier switch, an auxiliary switch, anoperating power capacitor and a rectifier controller. The rectifierswitch is electrically connected to the auxiliary switch. An operatingpower voltage is across the operating power capacitor to supply power tothe rectifier controller. When the rectifier controller turns OFF boththe rectifier and auxiliary switches, the rectifier circuit supports afirst loop, along which a first current is directed to flow into therectifier circuit from the anode node, through the operating powercapacitor, and away the rectifier circuit from the cathode, so theoperating power capacitor is charged. When the rectifier controllerturns ON both the rectifier and auxiliary switches, the rectifiercircuit supports a second loop, along which a second current is directedto flow into the rectifier circuit from the anode node, through therectifier switch, and away the rectifier circuit from the cathode,without charging the operating power capacitor.

In case that the rectifier controller determines that the operatingpower voltage is high enough, the rectifier circuit supports the secondloop to perform rectification using the turned-ON rectifier switch withlow impedance. When the rectifier controller determines that theoperating power voltage is riskily low, it supports the first loop tocharge the operating power capacitor and raise the operating powervoltage. Please note that the current the rectifier circuit conductsalways flows from the anode node to the cathode to providerectification, no matter the rectifier circuit is supporting the firstloop or the second loop.

Embodiments of the invention also provide a power converter with atransformer, a power switch, and a synchronous rectifier circuit. Aprimary winding of the transformer is in series connected with the powerswitch between two input power lines. The synchronous rectifier circuitis in series connected with a secondary winding of the transformerbetween two output power lines. The synchronous rectifier circuit has arectifier switch, an auxiliary switch, a synchronous rectifiercontroller, and an operating power capacitor. The synchronous rectifiercontroller detects a demagnetization time of the transformer duringwhich the transformer is demagnetizing, and accordingly controls therectifier and auxiliary switches. A portion of the demagnetization timeis designated as a charge time, and another a rectification time. Duringthe charge time, the synchronous rectifier controller turns OFF both therectifier and auxiliary switches, so that a secondary-side current fromthe secondary winding of the transformer is directed to charge theoperating power capacitor, and to build up the operating power voltageacross the operating power capacitor. During the rectification time,nevertheless, the synchronous rectifier controller turns ON both therectifier and auxiliary switches, and the rectifier switch conducts thesecondary-side current from the secondary winding without charging theoperating power capacitor.

As the transformer is demagnetizing, the energy the transformer isreleasing is used to build up the operating power voltage during thecharge time. By this way, the operating power voltage could beindependently charged, and could not be affected by an over-low outputpower voltage of the power converter. During the rectification time, therectifier and auxiliary switches cooperate to perform rectification.

The rectifier switch according to some embodiments of the invention is aN-type MOS transistor having body and source electrically connected tothe source and the drain of the auxiliary switch, separately andrespectively. The rectifier switch according to other embodiments of theinvention is a N-type MOS transistor having both body and sourceelectrically connected to the source of the auxiliary switch.

In this specification, a switch is turned ON when it provides a shortcircuit with low impedance between two terminals of the switch; and isturned OFF when it provides an open circuit with high impedance betweenthe two terminals.

FIG. 1 demonstrates flyback power converter 100 according to embodimentsof the invention, having transformer TF, which includes, but is notlimited to include, primary winding PRM, secondary winding SEC, andauxiliary winding AUX, inductively coupling to each other. TransformerTF provides direct-current (DC) isolation between primary side S-PRM andsecondary side S-SEC. At primary side S-PRM, flyback power converter 100has primary winding PRM, power switch 20, power controller 18, auxiliarywinding AUX, diode DAUX and operating power capacitor CVDD. At secondaryside S-SEC, it has secondary winding SEC, synchronous rectifier circuit120 and output power capacitor COUT.

It could be understood that input power line IN and input power groundGND_(IN) are two input power lines, which in some embodiments of theinvention are two outputs from a bridge rectifier performing full-waverectification. Input power voltage V_(IN) at input power line IN mightbe as low as 90V or as high as 240V. Power switch 20 and primary windingPRM are electrically connected in series between input power line IN andinput power ground GND_(IN). Synchronous rectifier circuit 120 andsecondary winding SEC are electrically connected in series betweenoutput power line OUT and output power ground GND_(OUT), while outputpower capacitor COUT has two ends connected to output power line OUT andoutput power ground GND_(OUT), respectively.

Power controller 18 generates PWM signal S_(DRV) to turn ON and OFFpower switch 20. When power switch 20 is turned ON, input power voltageV_(IN) energizes primary winding PRM, increasing the amplitude of itsmagnetic field therein. When power switch 20 is turned OFF, transformerTF demagnetizes, releasing the energy it has stored to output powercapacitor COUT and/or operating power capacitor CVDD via secondarywinding SEC and/or auxiliary winding by way of the rectificationprovided by rectifier circuit 120 and/or diode DAUX. This period of timewhen transformer TF demagnetizes to release energy is nameddemagnetization time TDEG. Output power voltage V_(OUT) across outputpower capacitor COUT is for supplying power to a load not shown in FIG.1 , while operating power voltage V_(DD) across operating powercapacitor CVDD is for supplying power to power controller 18. Outputpower voltage V_(OUT) might be monitored by an error amplifier tosignal, via a photo coupler for example, power controller 18, whichaccordingly adjusts the ON time of power switch 20, so as to regulateoutput power voltage V_(OUT).

Synchronous rectifier circuit 120 has anode node PP, cathode node NN,and charge node CHG, capable of providing rectification between anodenode PP and cathode node NN. In other words, when the voltage at anodenode PP is higher than that at cathode node NN, synchronous rectifiercircuit 120 could provide a short circuit connecting anode node PP andcathode node NN, and if the voltage at anode node PP is lower than thatat cathode node NN it provides an open circuit separating anode node PPfrom cathode node NN. It is shown in FIG. 1 that anode node PP iselectrically connected to output power ground GND_(OUT), cathode node NNto secondary winding SEC, and charge node CHG to output power line OUT.

FIG. 2 shows synchronous rectifier circuit 120A, an example ofsynchronous rectifier circuit 120. Synchronous rectifier circuit 120Ahas rectifier switch NSR1, auxiliary switch NC, rectifier controller102, operating power capacitor CSR, diode DSR, and schottky barrierdiode DSK, connection of which is demonstrated in FIG. 2 .

Rectifier switch NSR1 shown in FIG. 2 is an N-type MOS transistor withdrain D, body B, source S and gate G. It is understood that body B inFIG. 2 does not short to source S, so the body voltage at body B couldbe different from the source voltage at source S. Parasitic insiderectifier switch NSR1 is bipolar junction transistor BJ1 with anemitter, a base and a collector electrically connected to drain D, bodyB and source S of rectifier switch NSR1, respectively. The anode and thecathode of schottky barrier diode DSK are connected to body B and drainD respectively. Schottky barrier diode DSK is used to clamp thebody-to-drain voltage between body B and drain D, making it less than0.5V, so that bipolar junction transistor BJ1 cannot work under anactive mode and the source voltage at source S could be DC isolated fromdrain voltage V_(D) at drain D. Otherwise, if the body-to-drain voltageis more than 0.7V, then bipolar junction transistor BJ1 could operate atan active mode, and it would strongly pull the source voltage at sourceS and drain voltage V_(D) at drain D close to each other.

Across operating power capacitor CSR is operating power voltageVSR_(DD). As shown in FIG. 2 , connected between power line VDDSR andvirtual ground GND_(SR) is operating power capacitor CSR, supplying thepower that synchronous rectifier controller 102 needs for normaloperation. The voltage at virtual ground GND_(SR) is deemed to be 0V, aground voltage, that synchronous rectifier controller 102 references forprocessing signals.

Drain D of rectifier switch NSR1 is connected to cathode node NN, sourceS to anode node PP, and body B to virtual ground GND_(SR). Auxiliaryswitch NC has drain and source respectively connected to anode node PPand virtual ground GND_(SR), capable of optionally shorting anode nodePP to virtual ground GND_(SR). Diode DSR is between charge node CHG andpower line VDDSR, for directing current to charge operating powercapacitor CSR if diode DSR is forward biased. Rectifier controller 102detects drain voltage V_(D) at drain D of rectifier switch NSR1, toresponsively generate signals V_(G) and V_(CHG) controlling rectifierswitch NSR1 and auxiliary switch NC respectively.

FIG. 3 demonstrates synchronous rectifier controller 102, and FIG. 4shows control method M01 in use of synchronous rectifier circuit 120A.Synchronous rectifier controller 102 includes, but is not limited toinclude, demagnetization detector 103 and comparator 104.

In step S01 of control method M01, demagnetization detector 103 in FIG.3 detects whether transformer TF is demagnetizing, by sensing drainvoltage V_(D) at detection node DET. According to some embodiments ofthe invention, demagnetization detector 103 deems transformer TF asbeing demagnetizing or the current moment being within demagnetizationtime TDEG if drain voltage V_(D) is less than the virtual ground voltageat virtual ground GND_(SR). In the opposite, if drain voltage V_(D)becomes larger than the virtual ground voltage at virtual groundGND_(SR), demagnetization detector 103 deems the demagnetization oftransformer TF stops, demagnetization time TDEG being concluded.Depending on the determination whether the present moment is within oroutside demagnetization time TDEG, in together with the comparisonresult from comparator 104, demagnetization detector 103 providessignals V_(G) and V_(CHG). During demagnetization time TDEG, theelectrical energy stored by transformer TF is released to the secondaryside, demagnetizing, and secondary-side current I_(SEC) from secondarywinding SEC charges output power capacitor COUT and/or operating powercapacitor CSR.

In step S02, comparator 104 in FIG. 3 checks if operating power voltageVSR_(DD) is over low that synchronous rectifier controller 102 ispossibly going to fail if operating power voltage VSR_(DD) continuesdecreasing. Comparator 104, having hysteresis, compares operating powervoltage VSR_(DD) with reference voltage V_(SET-H) or V_(SET-L). Onlywhen operating power voltage VSR_(DD) rises above reference voltageV_(SET-H), 10V for instance, then comparator 104 has its output S_(COMP)become “1” in logic, meaning that operating power voltage VSR_(DD) isgood and healthy. Only when operating power voltage VSR_(DD) drops belowreference voltage V_(SET-L), 5.5V for instance, then comparator 104 hasits output S_(COMP) become “0” in logic, meaning that operating powervoltage VSR_(DD) is over low, or at risk.

In step S03, demagnetization detector 103 assigns a portion ofdemagnetization time TDEG to be charge time TB, during whichsecondary-side current I_(SEC), the current induced due todemagnetization, is directed to charge operating power capacitor CSR.For example, if output S_(COMP) is “0” in logic, implying the risk ofover-low operating power voltage VSR_(DD), demagnetization detector 103takes a beginning portion of demagnetization time TDEG as charge timeTB, during which demagnetization detector 103 turns OFF both rectifierswitch NSR1 and auxiliary switch NC, using signals V_(G) and V_(CHG).FIG. 5A demonstrates loop LPA that secondary-side current I_(SEC)follows when rectifier switch NSR1 and auxiliary switch NC are turnedOFF during charge time TB. Synchronous rectifier circuit 120A supportsto form loop LPA providing a charge path for powering operating powercapacitor CSR. Following loop LPA, secondary-side current I_(SEC) startsfrom secondary winding SEC, goes inside synchronous rectifier circuit120A via charge node CHG, passes through diode DSR, charges operatingpower capacitor CRS, passes schottky barrier diode DSK, leaves awaysynchronous rectifier circuit 120A via cathode node NN, and eventuallyreturns to secondary winding SEC.

In step S04 in FIG. 4 , demagnetization detector 103 assigns anotherportion of demagnetization time TDEG to be rectification time TOUT,during which secondary-side current I_(SEC) is directed to charge outputpower capacitor COUT, without charging operating power capacitor CRS.According to some embodiments of the invention, demagnetization detector103 takes the rest of demagnetization time TDEG after the end of chargetime TB as rectification time TOUT, during which demagnetizationdetector 103 turns ON both rectifier switch NSR1 and auxiliary switchNC, using signals V_(G) and V_(CHG). FIG. 5B demonstrates loop LPB thatsecondary-side current I_(SEC) follows when rectifier switch NSR1 andauxiliary switch NC are turned ON during rectification time TOUT. LoopLPB provides a charge path for charging output power capacitor COUT.Following loop LPB, secondary-side current I_(SEC) starts from secondarywinding SEC, charges output power capacitor COUT, goes insidesynchronous rectifier circuit 120A via anode node PP, passes throughrectifier switch NSR1, leaves away synchronous rectifier circuit 120Avia cathode node NN, and eventually returns to secondary winding SEC. InFIG. 5B, body B and source S of rectifier switch NSR1 short to eachother because auxiliary switch NC is turned ON. It is also demonstratedin FIG. 5B that secondary-side current I_(SEC) does not go throughauxiliary switch NC, even though auxiliary switch NC is turned ON.

FIG. 6A shows waveforms of signals in FIGS. 5A and 5B when operatingpower voltage VSR_(DD) is deemed over low, or operating power voltageVSR_(DD) is less than reference voltage V_(SET-L). From top to bottom,the waveforms in FIG. 6A are of PWM signal S_(DRV) controlling powerswitch 20 at primary side S-PRM, secondary-side current I_(SEC) fromsecondary winding SEC, current I_(S) charging output power capacitorCOUT, signal V_(G) controlling rectifier switch NSR1, current I_(B)charging operating power capacitor CSR, signal V_(CHG) controllingauxiliary switch NC, voltage V_(SEC) across secondary winding SEC, anddrain voltage V_(D) at drain D of rectifier switch NSR1, respectively.

At moment t00 in FIG. 6A, since drain voltage V_(D) abruptly drops tobecome negative, demagnetization detector 103 determines transformer TFis demagnetizing, and moment t00 is the beginning of demagnetizationtime TDEG.

The example shown in FIG. 6A has charge time TB and demagnetization timeTDEG start at the same time. During charge time TB, demagnetizationdetector 103 uses signals V_(G) and V_(CHG) to turn OFF both rectifierswitch NSR1 and auxiliary switch NC. As demonstrated in FIG. 6A, duringcharge time TB, from moment t00 to moment t01, operating power capacitorCSR is charged because current I_(B) is positive, and output powercapacitor COUT is not charged because current I_(S) is zero. It is alsoshown in FIG. 6A that during charge time TB voltage V_(SEC) acrosssecondary winding SEC equals to about operating power voltage VSR_(DD)across operating power capacitor CSR.

The example shown in FIG. 6A demonstrates that rectification time TOUTfollows right after charge time TB, and ends with the end ofdemagnetization time TDEG. According to embodiments of the invention,demagnetization detector 103 determines demagnetization time TDEG comesto an end at the time when drain voltage V_(D) becomes positive.

During rectification time TOUT, demagnetization detector 103 usessignals V_(G) and V_(CHG) to turn ON both rectifier switch NSR1 andauxiliary switch NC. As demonstrated in FIG. 6A, during rectificationtime TOUT, from moment t01 to moment t02, operating power capacitor CSRis not charged because current I_(B) is zero, and output power capacitorCOUT is charged because current I_(S) is positive. Therefore, it is alsoshown in FIG. 6A that during rectification time TOUT voltage V_(SEC)across secondary winding SEC equals to about output power voltageV_(OUT) across output power capacitor COUT.

The example in FIG. 6A has rectifier switch NSR1 turned ON only duringrectification time TOUT to perform rectification, while auxiliary switchNC is always turned ON except the duration of charge time TB. Whenauxiliary switch NC is ON, virtual ground GND_(SR) is considered asbeing shorted to output power ground GND_(OUT), so virtual groundGND_(SR) and output power ground GND_(OUT) are substantially the sameground. In other words, virtual ground GND_(SR) is DC isolated fromoutput power ground GND_(OUT) only during charge time TB, to letoperating power capacitor CSR being charged.

FIG. 6B shows waveforms of signals in FIG. 5B when operating powervoltage VSR_(DD) is good enough, or operating power voltage VSR_(DD) ishigher than reference voltage V_(SET-H). From top to bottom, thewaveforms in FIG. 6B are of PWM signal S_(DRV), secondary-side currentI_(SEC), current I_(S) charging output power capacitor COUT, signalV_(G) controlling rectifier switch NSR1, current I_(B) chargingoperating power capacitor CSR, and signal V_(CHG) controlling auxiliaryswitch NC, respectively. Simply speaking, as long as operating powervoltage VSR_(DD) is good enough, operating power capacitor CSR need notbe charged, and the whole demagnetization time TDEG is only used forsynchronous rectification. It can be observed in the embodiment of FIG.6B that auxiliary switch NC is turned ON at all time to short virtualground GND_(SR) to output power ground GND_(OUT), and that rectifierswitch NSR1 is only turned on during demagnetization time TDEG. In FIG.6B rectification time TOUT is the same with demagnetization time TDEG.

It is merely a design choice that charge time TB and demagnetizationtime TDEG in FIG. 6A begin at the same time, and is not intended tolimit the scope of the invention. Charge time TB could be any portion ofdemagnetization time TDEG. According to an embodiment of the invention,rectification time TOUT and demagnetization time TDEG start at the sametime, charge time TB starts when rectification time TOUT ends, and bothcharge time TB and demagnetization time TDEG end together.

Some embodiments of the invention could have more than one charge timeTB within one demagnetization time TDEG. For example, first charge timeTB1 and demagnetization time TDEG start at the same time. Rectificationtime TOUT follows the end of first charge time TB1. Second charge timeTB2 starts after the end of rectification time TOUT, and ends at thesame time when demagnetization time TDEG ends.

According to embodiments of the invention, output power voltage V_(OUT)could be as low as 3.5V, and operating power voltage VSR_(DD) ismaintained to be more than 5.5V. Power conversion efficiency formaintaining operating power voltage VSR_(DD) will be superior because itis built up using the energy released from demagnetization oftransformer TF.

An embodiment of the invention allows output power voltage V_(OUT) beingregulated at any voltage within the range from 3.5V to 20V, whileoperating power voltage VSR_(DD) is maintained to be more than 5.5V. Itimplies that voltage V_(SEC) across secondary winding SEC has maximumsranging from 5.5V to 20V, about a 4-fold voltage variation range(˜20/5.5), and this will inductively build up operating power voltageV_(DD), that supplies power to power controller 18 in FIG. 1 , to varyabout within another 4-fold voltage variation range. In case that powercontroller 18 requires operating power voltage V_(DD) to have a minimumof 10V, power pin VDD of power controller 18 of this embodiment mightbeneficially need to tolerate a voltage as low as 40V.

According to embodiments of the invention, synchronous rectifier circuit120 also monitors output power voltage V_(OUT), and allocates a portionof demagnetization time TDEG to be charge time TB if operating powervoltage VSR_(DD) is less than the summation of a predetermined voltageand output power voltage V_(OUT). For example, synchronous rectifiercircuit 120 starts to introduce charge time TB into demagnetization timeTDEG if operating power voltage VSR_(DD) is not 5V higher than outputpower voltage V_(OUT). In other words, synchronous rectifier circuit 120keeps operating power voltage VSR_(DD) a predetermined voltage higherthan output power voltage V_(OUT). According to embodiments of theinvention, reference voltage V_(SET-L) in FIG. 3 is about the summationof 5.5V and output power voltage V_(OUT), and reference voltageV_(SET-H) is about the summation of 6V and output power voltage V_(OUT).

FIG. 7 demonstrates synchronous rectifier circuit 120B, an example ofsynchronous rectifier circuit 120. Synchronous rectifier circuit 120Bhas rectifier switch NSR1, auxiliary switch NC, synchronous rectifiercontroller 102, operating power capacitor CSR and diode DSR, connectionof which is shown in FIG. 7 . Some aspects in FIGS. 7 and 2 are similaror in common, and explanation of these aspects are omitted because theycould be comprehensible in view of the teachings regarding to FIG. 2 .Even though FIG. 7 lacks schottky barrier diode DSK in FIG. 2 , it mightas well include schottky barrier diode DSK connected between body B anddrain D of rectifier switch NSR1 in another embodiment of the invention.In synchronous rectifier circuit 120B of FIG. 7 , body B and source S ofrectifier switch NSR1 short to each other, both connected to virtualground GND_(SR), which is also connected to the source of auxiliaryswitch NC. The drain of auxiliary switch NC is connected to anode nodePP, which is connected to output power ground GND_(OUT).

Both synchronous rectifier controller 102 in FIG. 3 and control methodM01 in FIG. 4 are applicable to synchronous rectifier circuit 120B ofFIG. 7 .

FIG. 8A demonstrates loop LPC that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.7 are turned OFF during demagnetization time TDEG. Loop LPC provides acharge path for powering operating power capacitor CSR. Following loopLPC, secondary-side current I_(SEC) starts from secondary winding SEC,goes inside synchronous rectifier circuit 120B via charge node CHG,passes through diode DSR, charges operating power capacitor CRS, goesthrough bipolar junction transistor BJ1, leaves away synchronousrectifier circuit 120B via cathode node NN, and eventually returns tosecondary winding SEC. Loop LPC is also applicable when rectifier switchNSR1 in FIG. 7 is turned ON and auxiliary switch NC is turned OFF, onlyif bipolar junction transistor BJ1 is replaced with turned-ON rectifierswitch NSR1. In other words, to provide loop LPC, auxiliary switch NC inFIG. 7 is turned OFF during demagnetization time TDEG no matterrectifier switch NSR1 is turned ON or OFF.

FIG. 8B demonstrates loop LPD that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.7 are turned ON during demagnetization time TDEG. Loop LPD provides acharge path for powering output power capacitor COUT. Following loopLPD, secondary-side current I_(SEC) starts from secondary winding SEC,charges output power capacitor COUT, goes inside synchronous rectifiercircuit 120B via output power ground GND_(OUT) and anode node PP, passesthrough both auxiliary switch NC and rectifier switch NSR1, leaves awaysynchronous rectifier circuit 120B via cathode node NN, and eventuallyreturns to secondary winding SEC.

The waveforms in FIGS. 6A and 6B are also applicable for explaining theoperation of synchronous rectifier circuit 120B. Persons skilled in theart could understand the operation of synchronous rectifier circuit 120Bbased on the aforementioned teaching with regard to FIGS. 6A, 6B, 7, 8Aand 8B.

FIG. 9 illustrates flyback power converter 600 according to embodimentsof the invention. Similar or the same aspects between flyback powerconverter 600 in FIG. 9 and flyback power converter 100 in FIG. 1 arenot detailed herein because they are comprehensible based on theaforementioned teaching. Different from FIG. 1 , synchronous rectifiercircuit 620 in FIG. 9 lacks charge node CHG, through which synchronousrectifier circuit 120 in FIG. 1 is connected to output power line OUT.

Even though synchronous rectifier circuit 620 in FIG. 9 is connectedbetween output power ground GND_(OUT) and secondary winding SEC, butthis invention is not limited to. Another embodiment of the invention,for example, could have anode node PP of synchronous rectifier circuit620 connected to secondary winding SEC and cathode node NN connected tooutput power line OUT while output power ground GND_(OUT) shorts tosecondary winding SEC.

Synchronous rectifier circuit 620 in FIG. 9 has, but is not limited tohave, only two terminals. It is possible for synchronous rectifiercircuit 620 to replace a conventional diode according to embodiments ofthe invention.

FIG. 10 shows synchronous rectifier circuit 620A, an example ofsynchronous rectifier circuit 620 in FIG. 9 . Similar or the sameaspects between synchronous rectifier circuit 620A in FIG. 10 andsynchronous rectifier circuit 120A in FIG. 2 are not detailed hereinbecause they are comprehensible based on the aforementioned teaching.Diode DSR in FIG. 10 , different from the corresponding one in FIG. 2 ,is connected between anode node PP and operating power capacitor CSR.

FIG. 11A demonstrates loop LPE that secondary-side current I_(SEC),which is positive during demagnetization time TDEG, follows when bothrectifier switch NSR1 and auxiliary switch NC in FIG. 10 are turned OFFduring charge time TB. Loop LPE provides a charge path for charging bothoperating power capacitor CSR and output power capacitor COUT. Followingloop LPE, secondary-side current I_(SEC) starts from secondary windingSEC, charges output power capacitor COUT via output power line OUT andoutput power ground GND_(OUT), goes inside synchronous rectifier circuit620A via anode node PP, passes through diode DSR, charges operatingpower capacitor CSR, passes through schottky barrier diode DSK, leavesaway synchronous rectifier circuit 620A via cathode node NN, andeventually returns to secondary winding SEC.

FIG. 11B demonstrates loop LPF that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.10 are turned ON during demagnetization time TDEG. Loop LPF provides acharge path not charging operating power capacitor CRS. Following loopLPF, secondary-side current I_(SEC) starts from secondary winding SEC,charges output power capacitor COUT via output power line OUT and outputpower ground GND_(OUT), goes inside synchronous rectifier circuit 620Avia anode node PP, passes through rectifier switch NSR1, leaves awaysynchronous rectifier circuit 620A via cathode node NN, and eventuallyreturns to secondary winding SEC. In FIG. 11B, body B and source S ofrectifier switch NSR1 short to each other because auxiliary switch NC isturned ON. It is also demonstrated in FIG. 11B that secondary-sidecurrent I_(SEC) does not go through auxiliary switch NC, even thoughauxiliary switch NC is turned ON. It is also shown in FIG. 11B that,during demagnetization time TDEG, output power capacitor COUT ischarged, but operating power capacitor CRS is not.

FIG. 12 shows waveforms of signals in FIGS. 11A and 11B when operatingpower voltage VSR_(DD) is deemed over low, or operating power voltageVSR_(DD) is less than reference voltage V_(SET-L). Similar or the sameaspects between FIG. 12 and FIG. 6A are not detailed herein because theyare comprehensible based on the aforementioned teaching.

FIG. 12 , unlike FIG. 6A, shows the waveform of secondary-side currentI_(SEC) the same with that of current I_(S). It is because both loopsLPE and LPF pass through output power capacitor COUT, as indicated inFIGS. 11A and 11B. In other words, secondary-side current I_(SEC), ifpositive, always goes through output power capacitor COUT no matter thepresent moment is within charge time TB or rectification time TOUT.

Furthermore, FIG. 12 , unlike FIG. 6A, demonstrates that voltage V_(SEC)across secondary winding SEC is about the summation of operating powervoltage VSR_(DD) and output power voltage V_(OUT) during charge time TB.It is because output power capacitor COUT and operating power capacitorCSR are equivalently connected in series to be charged during chargetime TB.

It is merely a design choice that charge time TB and demagnetizationtime TDEG in FIG. 12 begin at the same time, and is not intended tolimit the scope of the invention. Charge time TB could be any portion ofdemagnetization time TDEG. According to an embodiment of the invention,rectification time TOUT and demagnetization time TDEG start at the sametime, charge time TB starts when rectification time TOUT ends, and bothcharge time TB and demagnetization time TDEG end together.

Some embodiments of the invention could have more than one charge timeTB within one demagnetization time TDEG. For example, first charge timeTB1 and demagnetization time TDEG start at the same time. Rectificationtime TOUT follows the end of first charge time TB1. Second charge timeTB2 starts after the end of rectification time TOUT, and ends at thesame time when demagnetization time TDEG ends.

According to an embodiment of the invention, operating power voltageVSR_(DD) for synchronous rectifier circuit 620A is maintained higherthan 5.5V, no matter how much output power voltage V_(OUT) is. Operatingpower voltage VSR_(DD) is efficiently built up because operating powercapacitor CSR is charged up by secondary-side current I_(SEC) whentransformer TF demagnetizes.

In case that output power voltage V_(OUT) is allowed to vary in therange between 3.5V to 20V and that operating power voltage VSR_(DD) iskept to be about 5.5V, it implies that voltage V_(SEC) across secondarywinding SEC has maximums ranging from 9V(=3.5V+5.5V) to 25.5V(20V+5.5V),about a 3-fold voltage variation range (˜25.5/9). This will helpoperating power voltage V_(DD), that supplies power to power controller18 in FIG. 1 , vary roughly within another 3-fold voltage variationrange. For example, if power controller 18 requires operating powervoltage V_(DD) to have a minimum of 10V, power pin VDD of powercontroller 18 of this embodiment might need only to tolerate an inputvoltage as low as about 30V.

FIG. 13 shows synchronous rectifier circuit 620B, an example ofsynchronous rectifier circuit 620 in FIG. 9 . Similar or the sameaspects between synchronous rectifier circuit 620B in FIG. 13 andsynchronous rectifier circuit 120B in FIG. 7 are not detailed hereinbecause they are comprehensible based on the aforementioned teaching.Diode DSR in FIG. 13 , different from the corresponding one in FIG. 7 ,is connected between anode node PP and operating power capacitor CSR.

FIG. 14A demonstrates loop LPG that secondary-side current I_(SEC),which is positive and occurs during demagnetization time TDEG, followswhen rectifier switch NSR1 and auxiliary switch NC in FIG. 13 are turnedOFF. Loop LPG provides a charge path for powering operating powercapacitor CSR. Following loop LPG, secondary-side current I_(SEC)charges output power capacitor COUT and operating power capacitor CRS atthe same time. Loop LPG is still applicable if rectifier switch NSR1 andauxiliary switch NC in FIG. 13 are turned ON and OFF respectively, butbipolar junction transistor BJ1 in FIG. 14A should be replaced byturned-ON rectifier switch NSR1.

FIG. 14B demonstrates loop LPH that secondary-side current I_(SEC)follows when both rectifier switch NSR1 and auxiliary switch NC in FIG.13 are turned ON during demagnetization time TDEG. Loop LPH provides acharge path not charging operating power capacitor CRS. Following loopLPH, secondary-side current I_(SEC) charges output power capacitor COUT,but leaves operating power capacitor CRS uncharged.

Each of synchronous rectifier circuits 620A and 620B could replace anyone of traditional diodes according to embodiments of the invention. Itnot only provides rectification that directs current flowing a one-waypath from anode node PP to cathode node NN, but also builds up by itselfoperating power voltage VSR_(DD) needed for its own operation.

According to an embodiment of the invention, rectifier switch NSR1 andschottky barrier diode DSK in FIG. 2 or 10 are formed together on amonocrystal chip packaged as high-voltage electric device NSA shown inFIG. 15 with 4 pins corresponding to drain D, body B, source S and gateG. Each of schottky barrier diode DSK and the junction between body Band drain D could have a breakdown voltage higher than 100V. Sincesource S and body B are configured to not short to each other, thesource voltage at source S is capable of being different from the bodyvoltage at body B.

FIG. 15 demonstrates high-voltage electric device NSA, in whichrectifier switch NSR1 and schottky barrier diode DSK are formed andintegrated on monocrystal chip 801. As shown in FIG. 15 , rectifierswitch NSR1 is a vertical N-type MOS transistor, having poly-siliconlayers 810 as gate G, back-side metal 802, N-type heavily-doped layer804 and N-type lightly-doped layer 806 as drain D, P-type lightly-dopedbody layers 808 and P-type heavily-doped layers 814 as body B, andN-type heavily doped layers 812 as source S. Via the help of metalinterconnection, gate G, drain D, body B, and source S arecorrespondingly connected to pins PNG, PND, PNB and PNS of anintegrated-circuit package. In FIG. 15 , metal layer 836 acts as theanode of schottky barrier diode DSK, and N-type lightly-doped layer 806as the cathode of schottky barrier diode DSK. Schottky barrier diode DSKfurther has p-type lightly-doped body layers 828 and p-typeheavily-doped layers 834, both electrically connected to metal layer836. Gap GP between two adjacent p-type lightly-doped body layers 828could be used to adjust the breakdown voltage of schottky barrier diodeDSK. It is comprehensible that p-type lightly-doped body layer 808 andp-type lightly-doped body layer 828 are formed by way of the sameprocess flow and the same process conditions, so they have the sameimpurity concentration and the same junction depth. Analogously, p-typeheavily-doped layers 814 and p-type heavily-doped layers 834 are formedby way of the same process flow and the same process conditions, so theyhave the same impurity concentration and the same junction depth.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

What is claimed is:
 1. A rectifier circuit, comprising: an anode nodeand a cathode node; an operating power capacitor, across which is anoperating power voltage; a rectifier switch and an auxiliary switch,electrically coupled to each other; and a rectifier controller, suppliedpower by the operating power capacitor for controlling the rectifierswitch and the auxiliary switch; wherein the rectifier controller turnsOFF the auxiliary switch to support a first loop, along which a firstcurrent flows from the anode node, through the operating powercapacitor, and to the cathode node, so as to charge the operating powercapacitor; the rectifier controller turns ON the auxiliary switch andthe rectifier switch to support a second loop different from the firstloop, where a second current, following the second loop, flows from theanode node, through the rectifier switch and to the cathode node withoutcharging the operating power capacitor; and the first and second loopare supported when the anode node is higher than the cathode node inview of voltage.
 2. The rectifier circuit of claim 1, wherein therectifier switch has a source, a drain, a gate and a body, the drain iselectrically connected to the cathode node, and the auxiliary switch iscapable of shorting the body to the anode node.
 3. The rectifier circuitof claim 2, wherein the body is electrically connected to the source. 4.The rectifier circuit of claim 2, wherein the source is electricallyconnected to the anode node, and the rectifier circuit further comprisesa schottky barrier diode connected between the body and the drain. 5.The rectifier circuit of claim 2, further comprising a diode connectedbetween the anode node and the operating power capacitor, and theoperating power capacitor is electrically connected between the diodeand the body.
 6. The rectifier circuit of claim 1, wherein the rectifiercontroller compares the operating power voltage with a reference voltageto control the auxiliary switch.
 7. A power converter, comprising: atransformer with a primary winding and a secondary winding; a powerswitch, connected in series with the primary winding between two inputpower lines; a synchronous rectifier circuit connected to the secondarywinding, the synchronous rectifier circuit comprising: a rectifierswitch, electrically connected between one of two output power lines andthe secondary winding; an auxiliary switch, electrically coupled to therectifier switch; a synchronous rectifier controller, for detecting ademagnetization time of the transformer to control the rectifier andauxiliary switches, wherein the demagnetization time includes a chargetime and a rectification time; and an operating power capacitor, acrosswhich is an operating power voltage, for supplying power to thesynchronous rectifier controller; wherein, during the charge time, thesynchronous rectifier controller turns OFF the auxiliary switch, and thesynchronous rectifier circuit directs a secondary-side current from thesecondary winding to charge the operating power capacitor; and duringthe rectification time, the synchronous rectifier controller turns ONthe rectifier and auxiliary switches, and the synchronous rectifiercircuit directs the secondary-side current to go through the rectifierswitch without charging the operating power capacitor.
 8. The powerconverter of claim 7, wherein the charge time substantially starts witha beginning of the demagnetization time.
 9. The power converter of claim7, wherein the charge time substantially ends with an end of thedemagnetization time.
 10. The power converter of claim 7, wherein duringthe rectification time the secondary-side current flows along a loopthrough the rectifier switch and the auxiliary switch.
 11. The powerconverter of claim 7, wherein during the rectification time thesecondary-side current flows along a loop through the rectifier switchwithout flowing through the auxiliary switch.
 12. The power converter ofclaim 7, wherein: the power converter comprises an output powercapacitor connected between the two output power lines; and during thecharge time the synchronous rectifier circuit directs the secondary-sidecurrent to charge both the output power capacitor and the operatingpower capacitor.
 13. The power converter of claim 7, wherein: the powerconverter comprises an output power capacitor connected between the twooutput power lines; and during the charge time the synchronous rectifiercircuit directs the secondary-side current to not charge the outputpower capacitor.
 14. The power converter of claim 7, wherein: thesynchronous rectifier controller turns ON the auxiliary switch when thepower switch is turned ON.
 15. A control method in use of a powerconverter supplying an output power voltage across two output powerlines, wherein the power converter comprises a transformer with aprimary winding and a secondary winding, and a synchronous rectifiercircuit connected to the secondary winding, the synchronous rectifiercircuit comprises a rectifier switch and an auxiliary switchelectrically coupled to each other, and the rectifier switch iselectrically connected between the secondary winding and one of twooutput power lines, the control method comprising: detecting ademagnetization time of the transformer to control the rectifier andauxiliary switches, wherein the demagnetization time comprises a chargetime and a rectification time; during the charge time, turning OFF theauxiliary switch, so as to direct a secondary-side current from thesecondary winding to charge an operating power capacitor that suppliespower to a synchronous rectifier controller controlling the rectifierand auxiliary switches; and during the rectification time, turning ONboth the rectifier and auxiliary switches, so as to direct thesecondary-side current from the secondary winding to build up the outputpower voltage and not charge the operating power capacitor.
 16. Thecontrol method of claim 15, comprising: turning OFF both the auxiliaryswitch and the rectifier during the charge time.
 17. The control methodof claim 15, wherein, during the charge time, the secondary-side currentcharges the operating power capacitor and builds up the output powervoltage at the same time.
 18. The control method of claim 15, wherein,during the charge time, the secondary-side current charges the operatingpower capacitor and does not build up the output power voltage.
 19. Thecontrol method of claim 15, wherein the charge time starts at abeginning of the demagnetization time.
 20. The control method of claim15, wherein the charge time ends at an end of the demagnetization time.